Behavior of direct reduced iron and hot briquetted iron in the upper blast furnace shaft: part II. A model of oxidation

The high-temperature properties of the ferrous burden in the cohesive zone of the blast furnace (BF) are a function of its history in the upper shaft. It is considered that charging direct reduced iron (DRI) and hot briquetted iron (HBI) into the BF increases its efficiency and productivity. However, oxidation of DRI and HBI can occur in the low-temperature zone in the BF, which may affect their softening and melting properties. This work was designed to estimate the oxidation degree of DRI/HBI in the upper BF shaft. In this article, a model of oxidation was developed, which predicted that DRI and HBI can be oxidized up to 10 and 2 pct, respectively. The model was then put forth to a laboratory-simulated test and industrial simulated blast furnace (SBF) test for its verification. The results of SBF tests indicated that the oxidation of DRI/HBI occurs in a temperature range of 700 degrees C to 950 degrees C with the gas compositions used for the tests. The morphology of iron in DRI is expected to exhibit Fe-FeO-Fe layers in varying thickness at the beginning of the cohesive zone. The oxidation in HBI briquettes is primarily limited to its external surface. These results indicate that the impact of oxidation of DRI/HBI on the cohesive zone will not be significant.